Dynamo



(No Model.)

W. H. ELKINS.

DYNAMO.

No. 460,372. Patented Sept. 29, 1891.

IVILLIAM HENRY ELKINS, OF CAMBRIDGE, MASSACHUSETTS, ASSIGNOR, BY

DIRECT AND MESNE ASSIGNMENTS, TO THE AMERICAN ELECTRIC MA- CHINERYCOMPANY, OF PORTLAND, MAINE.

DYNAMO.

SPECIFICATION forming part of Letters Patent No. 460,372, datedSeptember 29, 1891. Application filed November 28, 1890. Serial No.372,839. (No model.)

To all whom it may concern.-

Be it known that I, WILLIAM HENRY EL- KINs, of Cambridge, in the countyof Middlesex and State of Massachusetts, have invented an Improvement inDynamos, of which. the following is a specification, reference being hadto the accompanying drawings, in which- Figure 1 is a diagramillustrating one form of myinvention. Figs. 2 and 3 are diagrams IO alsoillustrating my invention with slight modifications.

My invention is a dynamo with one coil or set of coils for the north andanother for the south pole, which differ materially in the number ofturns, the terminals of the field-coil, having the greater number ofturns, being connected one to one of the main brushes and the other toan auxiliary brush, and the coil of the other pole forming a part of themain or work circuit.

B indicates the commutator, B the armature, and D D the main brushes,all as usual. The extra brush D is placed near the brush D, and thebrushes D and D are in electrical connection through the field-coil A bymeans of the conductors a and a, conductor a connecting one terminal offield-coilA with brush D and conductor a connecting the other terminalof field-coil A with brush D or, what is the same in substance, withthat part of the work-circuit between D and the translating devices inthe workcircuit. The main or work circuit is from brush D or from thejunction of conductor a with the 3 5 conductor from brush D to mainbrush D and through field-coil A and the lamps or other translatingdevices.

The operation is as follows: The brushes D D are adjusted at full load,so that a certain portion of the current in the main circuit is supplieddirectly by brush D and the other portion by brush D through field-coilA. For example, if a constant current of ten amperes is required in thework-circuit from D to D, I prefer to so adjust brushes D and D thatthere will be a current of five amperes from the commutator B throughbrush D and five amperes from the commutator through brush D, conductora, field-coil A, and conductor a, these two currents uniting at thejunction of conductor a with the work-circuit. If now one lamp be outout or the resistance of the work-circuit decreased, the current willtend to increase above the ten amperes desired; but if the brush D bemoved toward the brush D or vice versa, the current through the circuita A a will be decreased and the field weakened, as A is one of thefield-coils. IVhile the mere motion of the brushesDD to bring themnearer together reduces the current in circuit a A a, the reduction ofthat current weakens the field, and this in turn reduces the differenceof potential between the highest and lowest points in the commutator,which still further reduces the current in circuit a A a, so that aslight approach of the brushes D D produces a marked effect. Thisreduction of the field strength also alters the distribution of thetotal current, for if the current in a A a be red need to four amperesthe current supplied to the main circuit directly from brush D must besix amperes, in order to keep a constant current of ten amperes in themain circuit. These figures are of course for explanation merely, and Iuse them simply because I have found in practice that my dynamo worksadmirably with five amperes in the regulating-circuit a A a when at fullload and with a constant current of ten amperes in the work-circuit. Inthat case for symmetry I make the coil A with twice as many turns as thecoil A; but this is obviously a detail of construction which may bevaried, as will be clear to all skilled in the art. The number of turnsin coil A relatively to those in coil A will not in practice need to bemore than two to one, and may well be three to two or four to three. Thegist of the matter is to divide the current in the work-circuit into twoparts, one of 0 which is variable and passes through the coil of onepole-in this case the coil or set of coils indicated by A-while theother is kept con stant by variations in the first and passes throughthe work-circuit of which the coil of 5 the other polein this case thatindicated by Aforms a part.

My theory is that the difference of potential between the brushes D andD is sufficient, in view of the resistance in the circuit a A a, to givethe current desired through field coil A, and that by shifting brush Dtoward brush D the current in the regulating-circuit a A a is varied byvarying the difference of potential between brushes D and D The simplestway to vary the current through the regulating-circuit a A a is to moveone of the brushes D or D and I prefer to move the brush D. The movementof D from the point of maximum potential to a point of lower potentialon the commutator B will reduce the current through theregulating-circuit, and vice versa,if D be stationary; but the movementof D from a higher to a lower potential will increase the currentthrough the regulating-circuit, and vice versa, if D be stationary; butcertain practical objections exist to moving brush D and I thereforeprefer to move brush D to regulate the current in the regulating-circuit a A a. This regulating movement of either or both the brushes DD may obviously be by hand or by mechanism, as will be clear withoutfurther description.

Another way to vary the current through regulating-circuit a A a is touse a Variable resistance R in that circuit, as indicated in Fig. 2, forif R be very small practically the current through coil A will be thesame as in Fig. 1; but by increasing R either by hand or by mechanismthe current through coil A may be varied, as-before described.

A third way of varying the current through circuit a A a is by means ofa shunt-circuit c of which a variable resistance R forms a part, asindicated in Fig. 3. Here if R be very small practically no current willpass through coil A but if R be very large practically the same currentswill pass through A as if there were no shunt-circuit.

My dynamo, whether used as a generator or motor, can be regulated withfacility and accuracy, and will be found very sensitive, as a slightvariation in the current through the regulating-circuit, however caused,will suffice to keep the current in the work-circuit constant, althoughthe resistance in the workcircuit be considerably and suddenly varied. Ihave shown conductor a terminating at brush D ;v but it will be obviousthat it may connect with the main circuit at any point between D and thetranslating devices.

I am aware that it is not new to divide the current of a dynamo into twoparts and to vary one of the parts that passes through the whole or apart of the field-coil, as that is shown in Patent No. 336,962 to Tesla,dated March 2, 1886, and I disclaim all thatis shown in that patent; butin my dynamo the arm pore-turns in the field-coil of one pole are variedby varying the current through the regulating-circuit a A a, and thosein the fieldcoil of the opposite pole, which has always apractically-constant current, are practically constant. In short, in myinvention I control one pole only, and this is the distinguishingcharacteristic of my invention.

The main practical difficulty with all dynamos in which the current isdivided and a part of it only used to energize the field is that it isdifficult to prevent sparking at small loads. Moreover in all suchdynamos heretofore known the entire field required the full current atfull load; but in my invention that part of the field-coil in theregulating-circuit a A a never carries the full current, and I havediscovered that by regulating the current, energizing one pole only ofthe field, I practically prevent sparking, make the dynamo nearlyself-regulating, and can readily produce a practically-constant currentby a very slight variation of the regulating-current, in addition to theinstantaneous and automatic variation in the regulating-current producedby varying the load.

lVhat I claim as my invention is- 1. In a dynamo, the regulating-circuita A a through field-coil A on one leg of the fieldmagnet and containinga materially greater number, of turns than the other field-coil A, thework-circuit through coil A on the other leg of the field-magnet andcontaining a materially smaller number of turns than coil A, the mainbrushes D D, and the extra brush D the terminals of the main circuitbeing the extra brush D and the main brush D and the terminals of theregulating-circuit being the main brush D and that part of theworkcircuit near extra brush D all combined and operating substantiallyas described.

2. The method of regulating dynamos by dividing the main current intotwo portions, carrying both of those portions through the work-circuitand through a coil on one leg of the field-magnet, which coil has amaterially smaller number of turns than the coil on the other leg of thefield-magnet and carrying the other portion before it joins the firstthrough the latter coil, which has a materially greater number of turnsthan the former coil, all substantially as described.

\VILLIAM HENRY ELKINS.

lVitnesscs:

EDWARD S. BEACH, J OHN R. Snow.

IIO

